To extend the intrasanguinous host-mediated assay system to measure the organ distribution of mutagens in mice using Saccharomyces cerevisiae and Schizosacc-haromyces pombe as indicator organisms. The distribution of the yeast in the different organs will be measured as will the mutagenicity of various chemicals requiring metabolism to their active forms. The distribution of mutagen in the various organs will be determined and related to other in vivo effects of the chemical.